1. Field of the Invention
This invention is related to a method of forming bumps on wafers or substrates and in particular to one which is simple in operation and can be carried out at low cost.
2. Description of the Prior Art
Ball-Grid-Array (BGA), Chip-Size/Scale-Package (CSP) and Flip-Chip are the most popular of the newly developed packaging techniques and these techniques mostly rely on the flip chip mounting technology process. The broad meaning of flip chip mounting technology process is that the chip is first turned over and then affixed with its upper surface to a substrate via metal conductors. Generally, the metal conductors are referred to as metal bumps which are widely used in products in mass production because they are more reliable in manufacture than other means. The low cost bumping technology for forming the metal bump utilizes the electroless Ni/Au process to form a under-bump-metallurgy (UBM) layer first and then implants metal bumps thereon.
Referring to FIGS. 1axcx9c1h, a UBM layer 12 is first formed on the electrode pad on the upper side of the wafer 1 by the electroless Ni/Au method. Then, a layer of photo-resistant agent 2 is coated on the top of the wafer 1 and the heated. Thereafter, a mask 3 is arranged above the wafer 1 and then exposed to light to form a blind hole 21 above the UBM layer 12. Then, solder paste 5 is filled into the blind hole 21 by a pusher 4 and heated to melt and cool into a solder block 6. Then, the photo-resistant agent 2 is removed by a chemical agent and cleaned to leave a protruded solder block 6. Finally, the protruded solder block 6 is further heated to form a ball-shaped solder bump 7.
However, the photo-resistant agent, the exposure and the removal of the photo-resistant agent cause a lot of drawbacks in such a method. Firstly, it is necessary to allow a certain period of time for the drying of the photo-resistant agent. In addition, a mask is required for the exposure procedure, thereby increasing cost. Furthermore, the photo-resistant agent must be removed by a chemical agent, which makes the method more complicated, requires a longer time to complete the method, and therefore increases the manufacturing costs. Thus, it is an object of the present invention to provide a method of forming bumps on wafers or substrates which can obviate and mitigate the above-mentioned drawbacks.
This invention is related to a method of forming bumps on wafers or substrates and in particular to one which is simple in operation and can be carried out at low cost.
It is the primary object of the present invention to provide a method of forming bumps on wafers or substrates which utilizes the step of adhering synthetic tape on the wafer instead of the conventional method of filling a photo-resistant agent on the wafer, thereby eliminating the time required for the drying of the photo-resistant agent
It is another object of the present invention to provide a method of forming bumps on wafers or substrates which utilizes laser to punch holes on the synthetic tape to form a blind hole and then removes the synthetic tape after the solder paste is melted and cooled into a solder block, instead of using a mask and processing the photo-resistant agent with exposure treatment to form a blind hole on the wafer, thereby eliminating the cost of the mask and largely reducing the time required for this procedure.
According to a preferred embodiment of the present invention, the method of forming bumps on wafers or substrates includes the steps of adhering a heat-resistant and steady synthetic tape on the top of the wafer, punching holes through the synthetic tape to form a blind hole on the synthetic tape above the under-bump-metallurgy layer (UBM), filing solder paste into the blind hole by a pusher, melting and then cooling the solder paste into a solder block, removing the synthetic tape to expose the solder block, and melting the solder block to form a ball-shaped solder bump.
The foregoing objects and summary provide only a brief introduction to the present invention. To filly appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts. Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example.